The present invention relates to a disc library apparatus, more particularly to the sensing of the positions of discs and drives in the apparatus.
A disc library apparatus is a type of mass storage device having shelves on which discs are stored, at least one disc drive (hereinafter, simply xe2x80x98drivexe2x80x99) for accessing information on the discs, and a mechanism for automatically transporting a selected disc to and from a selected drive. The disc transport mechanism has a movable carrier with various sensors, including a position sensor for sensing the position of the carrier, a chucking sensor for sensing that a disc has been picked up, and a disc sensor for sensing the presence of a disc on a shelf, or the presence of a disc ejected from a drive. The disc sensor is conventionally a transmissive optical sensor that detects a disc when the disc interrupts a light path between a light-emitting element and a light-sensing element.
The apparatus also has a control unit with firmware stored in, for example, a read-only memory (ROM). The firmware includes programs that initialize the apparatus at power-up, control communication with a host device, control the disc transport sequence, handle errors, and carry out various other processing. The firmware also includes information giving the positions of the shelves and the position of each drive.
In commands from the host device, the shelves and drives are identified by addresses. When the control unit receives a command to use a designated drive to access information on a disc on a designated shelf, the control unit controls the disc transport mechanism so as to move the carrier to the known position of the designated shelf, pick up the disc, carry the disc to the known position of the designated drive, and insert the disc into the drive. These operations are repeated in reverse after the desired information has been accessed.
When a command of this type is executed, the addresses must be valid; that is, there must be a disc on the designated shelf, and the designated drive must be able to accept the disc. The presence of discs on shelves can easily change, as discs are added to or removed from the library. In many cases, the discs are stored in removable magazines, each having a plurality of shelves, so when a magazine is added, removed, or replaced, the status of a large number of shelves can change simultaneously. The control unit accordingly includes a read-write memory with a table of known disc locations. When a magazine is added or replaced, the control unit moves the carrier so that the disc sensor scans the magazine, detects the presence or absence of a disc on each shelf, and updates the table of disc locations accordingly.
This table enables the control unit to keep track of the locations of discs, but it does not facilitate the installation or removal of drives. Conventional firmware is coded on the assumption that the drives are permanently installed, and that their positions will not change. If a drive is removed, or a new drive is installed, or a drive is moved from one position to another, it becomes necessary to shut down the library apparatus and update the firmware, by replacing the ROM, for example. This creates considerable problems in the operation and maintenance of the apparatus.
Another type of problem occurs when a disc is ejected from a drive. If ejected too forcefully, the disc may damage the disc transport mechanism, or the disc itself may be damaged or dropped. If a disc drops to an unintended location, further problems such as electrical short circuits may occur. As a solution to these problems, a stopper is conventionally mounted together with each drive, positioned to prevent the disc from being ejected too far. This solution is imperfect, however, because the stopper may be bent or moved out of place after being installed, or may fail to be installed at all because of human forgetfulness.
The sensors are also a source of problems in that they constrain the mechanical design of the shelves, carrier, drives, and stoppers. In particular, the use of a transmissive optical sensor as the disc sensor imposes design constraints. Precise alignment of the light-emitting and light-sensing elements in this sensor is also necessary.
An object of the present invention is to prevent accidents caused by disc ejection.
Another object is to simplify the installation and removal of drives in a disc library apparatus.
Another object is to reduce design constraints due to sensors in a disc library apparatus.
A disc library apparatus according the present invention has shelves for storing discs, at least one drive for accessing information on a disc when the disc is loaded into the drive, and a carrier for carrying discs from the shelves to the drive.
According to a first aspect of the invention, a stopper is installed together with each drive, for restraining discs ejected from the drive. A disc sensor for detecting discs stored on shelves, detecting discs ejected from the drives, and detecting the stoppers is mounted on the carrier. A control unit controls the carrier and the drives, and disables the use of a drive if its stopper is not detected by the disc sensor. The control unit may also disable the use of a drive if its stopper is installed in an incorrect position, as detected by the disc sensor.
According to a second aspect of the invention, a disc sensor is mounted on the carrier. The control unit includes a memory unit and a processor unit. The memory unit stores drive information indicating the positions of installed drives, and disc information indicating the current positions of discs. The processor unit automatically acquires and updates the drive information and disc information by moving the carrier to the positions of the drives and shelves, using the disc sensor to detect the drives, detect discs ejected from drives, and detect discs stored on shelves, and receiving signals from the drives indicating the presence of loaded discs in the drives.
According to a third aspect of the invention, a reflective optical sensor is mounted on the carrier. The reflective optical sensor detects discs stored on the shelves, and discs ejected from the drives, and notifies a control unit that controls the carrier and drives. The same reflective optical sensor may also detect discs that have been picked up and are being carried by the carrier.
Accidents due to disc ejection are prevented by detecting the presence and absence of the stoppers, and by detecting whether the stoppers are correctly installed.
The installation and removal of drives is simplified by detecting the positions of installed drives and updating the drive information automatically.
Design constraints due to sensors are reduced by the use of a reflective optical sensor as the disc sensor.